Module that extracts contour lines from a raster. Algorithm comes from <a href="http://code.google.com/p/jai-tools/"> jai-tools</a>, which used <a href="http://local.wasp.uwa.edu.au/~pbourke/papers/conrec/"> the Conrec</a> contouring subroutine.
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<h3>Inputs</h3>
<ul>      
<li>the raster on which to calculate the contours</li>
<li>the minimum value for the contours</li>
<li>the maximum value for the contours</li>
<li>the contours interval</li>
</ul>
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<h3>Output</h3>
<ul>      
<li>the generated contour lines vector</li> 
</ul>
<h3>Notes</h3>
The module has a couple of known issues:
<ul>      
<li>it missbehaves if there are cell values that happen to be equal to the contour values (see above referenced article for further explanation).</li>
<li>isolines can accumulate at image borders</li>
</ul>